Electrostatic chucking (or E-chuck) is a technique used to secure a wafer onto a susceptor in a wafer processing chamber. In recently developed wafer processing technology, the electrostatic wafer holding technique is frequently used in which a chuck electrostatically attracts and holds a wafer. The E-chuck method is a highly desirable technique for use in the vacuum handling and processing of silicon wafers. In contrast to a conventional method by mechanical means such as clamping so that only slow motion of a wafer holder is allowed during wafer transfer, an E-chuck can hold wafers with a force equivalent to several tenths of Torr pressure. Since there are no moving parts acting on the wafer surface, there can be no particle generation or contamination problems in the process chamber.
Another advantage achieved by the electrostatic chuck is the avoidance of non-uniform clamping associated with mechanical clamping device. The E-chuck utilizes an attractive Coulomb force between oppositely charged surfaces to clamp together an article and a chuck. In an electrostatic chucking operation, the force acting between the wafer and the chuck is uniform between a flat wafer and a flat chuck, in contrast to the mechanical clamping system wherein clamping is effected only around the periphery of a wafer. Special provisions must be made in a mechanical clamping system to compensate for the bowing at the center of a wafer caused by the pressure of cooling gas which is pumped in between the wafer and the pedestal that holds the wafer. The bowing phenomena is eliminated in an E-chuck since the wafer is held on a substantially planar chuck surface with an even electrostatic force distributed according to the electrode layout. The electrostatic force is generally sufficient for preventing bowing of the wafer and for promoting uniform heat transfer over the entire wafer surface by flowing an inert gas flow between the wafer and the E-chuck.
A typical vacuum process chamber 10 for etching semiconductor wafers is shown in FIG. 1. The vacuum process chamber 10 is constructed by a lower chamber 12, an upper chamber 14 and a cathode assembly 16 which is part of an electrostatic chuck assembly 20. The process chamber 10 is covered by a dome 18 which forms a hermetically sealed chamber 14. A vacuum pumping channel 22 is provided for evacuating the chamber interior such that a semiconductor process can be carried out. Internal water cooling channels 26 are also provided for cooling the apparatus during operation of the chamber. Wafer lift bellows 28 which work in conjunction with wafer lift pins 32 lift wafers from the E-chuck 20 after the completion of an etch process. Cathode lift bellows 34 are utilized for the vertical movement of the cathode 16 and the E-chuck 20. A gas inlet 36 is utilized for feeding an inert gas through the cathode lift bellows 34 to the surface 24 of the E-chuck 20.
A perspective view of the components that make up the E-chuck assembly 20 is shown in FIG. 2. In the specific construction, the E-chuck 20 consists of a focus ring 40, a capture ring 42, a shell assembly 44, lift pins 46 which are installed onto a cathode 16 inside an upper chamber 48, and a bottom chamber 50. In the operation of the E-chuck 20, a wafer (not shown) is positioned on top of the surface 24 of the shell assembly 44. In the top surface 24, a plurality of ventilation holes 52 are provided which are located at the tips of passageways 54. The plurality of pin holes, or ventilation holes 52 are provided such that a cooling gas may be fed into the gap 19. between surface 24 of the shell assembly 44 and the wafer backside.
An enlarged, cross-sectional view of the shell assembly 44 for the E-chuck 20 positioned in a process chamber 10 is shown in FIG. 3. It should be noted that the E-chuck assembly 20 is shown greatly simplified to merely illustrate the present invention and thus the construction details of the E-chuck 20 are not repeated in FIG. 3. A cooling gas 60 of helium is fed into the gas passageway 54 and then flown into a gap between the E-chuck surface 24 and the wafer backside through vent holes 52. The function of the helium gas 60 is not only to cool the backside of a wafer, but also to achieve a more uniform temperature by transferring heat to the cathode.
In the conventional process chamber 10 shown in FIG. 3, the cooling gas of helium is fed into the E-chuck 20 through a control valve 56, a first conduit 58 and a second conduit 60 which are connected by a coupling 62. The first conduit 58 is normally constructed of a flexible metal pipe such as a pipe made of braided metal tape. The second conduit 60, for ease of installation, is normally supplied in a flexible, metal mesh reinforced elastomeric hoses. After repeated usage, the flexible metal pipe 58 may develop a leak such that the ventilation function of the helium gas cannot be satisfactorily performed since the pipe moves up-and-down with the cathode all the time. In order to replace a defective conduit 58, the upper chamber 14 must be vented to the atmosphere during the procedure. This becomes a time consuming and labor consuming to process and furthermore, the venting of the upper chamber 14 to the atmosphere further increases the possibility of chamber contamination.
Another frequently observed problem in the operation of an E-chuck is the blockage, or partial blockage of the vent holes 52. When the blockage is severe, the effectiveness of a helium cooling gas for achieving temperature uniformity on the wafer is greatly reduced. The plugging of the vent holes 52 may occur after a wet cleaning process is conducted on the E-chuck 20. Any cleaning residue may be lodged in the tiny vent holes 52 to form a partial or complete blockage of the holes. A wafer processed on the E-chuck 20 may thus be burned or heated non-uniformly due to the insufficient cooling by the helium cooling gas. This may result in the scrap of the wafer.
It is therefore an object of the present invention to provide an apparatus for servicing a wafer chuck that does not have the drawbacks or shortcomings of the conventional apparatus.
It is another object of the present invention to provide an apparatus for servicing an electrostatic chuck in a semiconductor process chamber that does not require the breaking of vacuum in the chamber.
It is a further object of the present invention to provide an apparatus for servicing an electrostatic chuck in a semiconductor process chamber that is capable of isolating the process chamber when a cooling gas supply line to the chamber is disconnected.
It is another further object of the present invention to provide an apparatus for servicing an electrostatic chuck in a semiconductor process chamber that includes a three-way valve and a high pressure inert gas supply.
It is still another object of the present invention to provide an apparatus for servicing an electrostatic chuck in a semiconductor process chamber which allows the cleaning of vent holes in the surface of the electrostatic chuck by a high pressure inert gas.
It is yet another object of the present invention to provide an apparatus for servicing an electrostatic chuck in a semiconductor process chamber that can be used to replace a gas supply conduit to the chamber when a leakage in the conduit is detected to be larger than 2 m Torr per minute.
It is still another further object of the present invention to provide a method for testing leakage in a gas supply conduit to a wafer chuck by utilizing a three-way control valve and a high pressure inert gas supply.
It is yet another further object of the present invention to provide a method for venting an electrostatic chuck in an etch chamber by utilizing a three-way gas control valve and a high pressure nitrogen gas supply.